Air bearing facilitating load/unload of a magnetic read/write head

ABSTRACT

An air bearing surface for use on a magnetic read/write head. The air bearing surface provides a stable flight profile while exhibiting exception load/unload characteristics through the use of a plurality of pads providing high pressure areas as well as a central cavity providing a sub-ambient pressure to counter the high pressure areas. The channel is set a predetermined distance from the leading edge of the air bearing, the predetermined distance being greater than with prior art designs. A channel extends from the leading edge to the cavity to allow airflow into the cavity. The channel and the set back of the cavity both act in conjunction to facilitate unloading of the air bearing by preventing excessive sub ambient pressures.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to air bearing slidersfor use in magnetic head assemblies and in particular to air bearingslider geometry.

[0003] 2. Background of the Invention

[0004] Magnetic disk drives are used to store and retrieve data fordigital electronic apparatuses such as computers. In FIGS. 1A and 1B, amagnetic disk data storage systems 10 of the prior art includes a sealedenclosure 12, a disk drive motor 14, a magnetic disk 16, supported forrotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20attached to an actuator spindle S2 of actuator 18. A suspension 22 iscoupled at one end to the arm 20, and at its other end to a read/writehead or transducer 24. The transducer 24 (which will be described ingreater detail with reference to FIG. 2A) typically includes aninductive write element with a sensor read element. As the motor 14rotates the magnetic disk 16, as indicated by the arrow R, an airbearing is formed under the transducer 24 causing it to lift slightlyoff of the surface of the magnetic disk 16, or, as it is termed in theart, to “fly” above the magnetic disk 16. Alternatively, sometransducers, known as “contact heads,” ride on the disk surface. Variousmagnetic “tracks” of information can be written to and/or read from themagnetic disk 16 as the actuator 18 causes the transducer 24 to pivot ina short arc as indicated by the arrows P. The design and manufacture ofmagnetic disk data storage systems is well known to those skilled in theart.

[0005]FIG. 2 depicts a magnetic read/write head 24 including a substrate25 above which a read element 26 and a write element 28 are disposed.Edges of the read element 26 and write element 28 also define an airbearing surface ABS, in a plane 29, which can be aligned to face thesurface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element26 includes a first shield 30, an intermediate layer 32, which functionsas a second shield, and a read sensor 34 that is located within adielectric medium 35 between the first shield 30 and the second shield32. The most common type of read sensor 34 used in the read/write head24 is the magnetoresistive (AMR or GMR) sensor which is used to detectmagnetic field signals from a magnetic medium through changingresistance in the read sensor.

[0006] In magnetic disk technologies, it is generally desired to achievehigher data recording densities. In the context of the air bearingslider, one way of achieving increased recording densities is bymaintaining a low flying height. Maintaining a low flying heightrequires that, pitch angle and roll angle be held constant over thewhole disk surface.

[0007] On the one hand, the read/write head 24 must fly at a sufficientheight to avoid frictionally related problems caused by physical contactduring data communication between the head 24 and the rapidly rotatingdisk 16. On the other hand, the head 24 should be made to fly as low aspossible to obtain the highest possible recording densities.Accordingly, it is preferred that the slider fly as close as possible tothe disk surface without actually contacting the disk surface. Aconstant flying height is preferably maintained, regardless ofvariations in tangential velocity of the disk 16 during flying, crossmovements of the head 24 during data search operations, and changes inskew angle in the case of rotary type actuators.

[0008]FIG. 3A is a schematic perspective view of a conventional taperedflat slider 300. Two rails 302 are formed in parallel at a predeterminedheight on a surface of a slim hexahedron body 304 to thus formlengthwise extending air bearing surface rails (ABS rails) 305. Atapered or sloped portion 306 is formed at each leading edge portion ofthe ABS rails 305. In such a structure, air within a very thin boundarylayer rotates together with the rotation of the disk due to surfacefriction. When passing between the rotating disk and the slider, the airis compressed by the sloped portion 306 on the leading edge of the ABSrails 305. This pressure creates a hydrodynamic lifting force at theramp section which is sustained through the trailing edge of the ABS,thus allowing the slider to fly without contacting the disk surface.

[0009] The conventional slider of this type suffers a drawback in thatthe flying height, pitch angle and roll angle vary considerablyaccording to the skew angle of the rotary type actuator, i.e. accordingto the radial position of the slider over the disk surface. In addition,rapid movement of the actuator arm 20 can cause variations insliderpitch. With reference to FIG. 3B, In order to overcome thesevariations in slider pitch and to ensure a stable and low level flyheight, prior art ABSs have been provided with a cross rail 308,oriented perpendicular to the direction of airflow and located towardthe leading edge of the slider. Such a cross rail serves to create anegative or sub-ambient pressure there behind which forces the sliderdownward. Ideally the downward pressure from the cross bar balances withthe upward forces under the rails and a stable fly height is achieved.

[0010] When the time comes to terminate use of the data storage system10 the head 24 must be stored. One prior method referred to in FIG. 3Cis known to those skilled in the art as contact start stop (CSS). Withthe CSS system, upon powering down the system 10, the head 24 lands uponthe disk 16. The disk of this system is provided with a landing zone310. The surface of the landing zone has small bumps, formed with alaser, which prevent the head from sticking to the surface of the disk.The remainder of the disk provides a data zone 312 on which data can berecorded or read. Since any area consumed by the landing zone detractsfrom available data zone area, in order to increase the total amount ofdata which can be stored on the disk 16 it is desirable to reduce oreliminate the landing zone 310 in order to increase the data zone.

[0011] With reference to FIG. 3D, one method for eliminating the needfor a landing zone 310, is called a load/unload system. A landing ramp314 is provided on which the suspension arm 22 can rest allowing thehead 24 to suspend in mid air during non-use. This method advantageouslyprotects the head 24 and recording medium 16 by eliminating the need tocontact the head with the medium. However, this method creates otherproblems in that during unload of the head 24 from the recording medium16 the sub-ambient pressure tends to resist unloading of the head.

[0012] As the head 24 is lifted from the recording medium 16, the highpressure and sub-ambient pressure under the air bearing surface bothdecrease. However, prior art air bearing designs exhibit an unequalreduction of the pressures as the head 24 is unloaded. The sub-ambientpressures tend to decrease at a significantly lower rate than the highpressures as the distance between the head 24 and the recording medium16 increases. This creates a net sub-ambient force during unload. Insome cases the sub ambient force can be sufficient to cause plasticdeformation of the head suspension 22, permanently damaging the system10, and can cause dimpling of the recording medium 16. Furthermore, theexcessive sub-ambient pressure can cause a spring back effect when thesub-ambient pressure is finally overcome, causing the head 24 toseverely impact the recording medium 16 damaging both the recordingmedium and the head.

[0013] Thus there remains a need for an ABS having exceptional flightprofile characteristics which also exhibit good load and unloadcharacteristics. Such a head would not experience excessive sub-ambientpressures during unload and would preferably be useable in either CSS orload/unload systems.

SUMMARY OF THE INVENTION

[0014] The present invention provides an air bearing surface (ABS) foruse with a magnetic read/write head. The air bearing surface includes apair of side rails defining there between a channel. The channelterminates at its back end in a cavity also defined between the siderails, and a pressure pad is provided adjacent the trailing edge of theABS. The cavity of air bearing surface is set at a predetermineddistance from the leading edge of the air bearing, the predetermineddistance being greater than found in prior art air bearings. The channeland the cavity location both act to reduce sub-ambient pressureexperienced under the air bearing during unload of the read/write head.

[0015] A pair of front pads are provided located near the front of eachside rail. The pressure pads provide lift and also control the pitch ofthe ABS. In addition, a pair of central pads provided on the side railsmidway between the front and rear ends, provide additional lift and helpto control pitch and roll of the ABS. The side rails terminate in a pairof rear pads, one on each side rail, which are separated from thecentral pads by a gap. The rear pads, like the central pads, help tocontrol pitch and roll, to provide a stable flight profile, and the gapallows air to flow there through which facilitates stable flight whenthe head is flying at a skewed angle.

[0016] The trailing edge pad is the location of highest pressure underthe air bearing and provides most of the lift. The trailing edge padincludes a step which helps to increase the pressure thereunder. Thestep can terminate at its trailing edge in either an abrupt edge or asmooth ramp.

[0017] An alternate embodiment of the ABS has the front and central padsconnected by a bridge. Such a bridge is useful in circumstances whereincreased pitch is desired. In yet another embodiment, the depth of thecavity can be increased in order to provide additional sub-ambientpressure when necessitated by design parameters such as a need for alower flying height.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings, withlike reference numerals designating like elements.

[0019]FIG. 1A is a partial cross-sectional front elevation view of amagnetic data storage system;

[0020]FIG. 1B is a top plan view taken along line 1B-1B of FIG. 1A;

[0021]FIG. 2 is a cross-sectional view of a read write head of the diskdrive assembly of FIGS. 1A and 1B;

[0022]FIG. 3A is a perspective view of a prior art air bearing of a readwrite head;

[0023]FIG. 3B is a perspective view of a prior art air bearing of a readwrite head;

[0024]FIG. 3C is a perspective view of a contact start stop magneticdata storage system

[0025]FIG. 3D is a perspective view of a load/unload magnetic datastorage system;

[0026]FIG. 4 is a perspective view of an air bearing of the presentinvention;

[0027]FIG. 5 is a partial side view taken along line 5-5 of FIG. 4;

[0028]FIG. 6 is a partial side view similar to FIG. 5 of an alternateembodiment of the invention;

[0029]FIG. 7 is a side view taken along line 7-7 of FIG. 4;

[0030]FIG. 8 is a schematic of a process including step formanufacturing the present invention;

[0031]FIG. 9 is a perspective view, similar to FIG. 4, of an alternateembodiment of an air bearing;

[0032]FIG. 10A is a graph illustrating the unload characteristics of aprior art air bearing;

[0033]FIG. 10B is a graph illustrating exemplary unload characteristicsof an air bearing of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] With reference to FIG. 4, a preferred embodiment of the presentinvention is embodied in a read/write head 400 in the form of agenerally rectangular ceramic block having a surface thereof configuredas an air bearing surface (ABS) generally referred to as 402, having aleading edge 403 at its front end and a trailing or edge 405 at its rearend. Description of the ABS can be best facilitated with reference toabase elevation 404 from which various features protrude. The ABS 402 isprovided with a pair of side rails 406 and a trailing edge pad 408.

[0035] The side rails 406 define there between a channel 410 at theportion of the rails nearest the leading edge 403. The channel has awidth W, which can be constant or variable along its length, the channelof the preferred embodiment being variable along its length. Midwayalong the length of the side rails the channel 410 terminates opening toform a cavity 412 between the side rails. The cavity is formed by asignificant narrowing of each side rail 406 as the side rails follow theedges of the ABS toward their rear ends. The side rails 406 create ahigh pressure area and are critical for providing a stable ABS 402.There must be sufficient surface area of the center rails to allow theair bearing to fly. Furthermore, increasing the surface area of the siderails 406 will increase the fly height of the ABS 402.

[0036] The cavity provides a sub ambient pressure under the ABS 402during operation of the system 10. The sub ambient pressure keeps theABS in close proximity to the magnetic medium 16 during operation of thedisk drive and helps to maintain a stable fly height. However, asdiscussed previously in the background of the invention, an excessivesub ambient pressure can cause problems during unload. A feature of thepreferred embodiment of the invention is that the cavity 412 is locatedfurther from the leading edge than with prior art designs. This set backof the cavity moves the center of sub-ambient pressure further back onthe ABS 402 which increases pitch and reduces the sub-ambient pressureunder the ABS 402 during unloading. This rearward positioning of thecavity is, however, limited by desired flight profile characteristics.The amount of cavity set back can be increased with increasing diskspeed without sacrificing performance. In some cases the set back can beas great as 25%.

[0037] In addition the sub-ambient pressure can be controlled, however,by adjusting the width W of the channel 410. A widening of the channelwill reduce the sub-ambient pressure, whereas narrowing the channel willincrease the sub-ambient pressure created by the cavity 412. As theread/write head 400 moves from the outer diameter to the inner diameterof the disk during operation, the speed of airflow generated under theABS 402 will decrease in direct proportion. An optimum balance of subambient and high pressure is obtained when there is negligibledifference in fly height between the inner and outer diameters of thedisk.

[0038] The channel width can vary from 3 mil to 15 mil as necessitatedby design parameters such as the speed of the disk 16 on which the ABS402 is to be used. However, it has been found that a channel width W of8 mils on a 40 mil wide read/write head 400 provides an optimumsub-ambient pressure in the cavity 412 for most applications and diskdrive speeds. The floor of the channel 410 and cavity 412 are both atthe level of the base elevation 404.

[0039] With continued reference to FIG. 4, the configuration of thechannel and cavity prevent accumulation of debris on the ABS 402. Priorart read/write heads have experienced the drawback that the sub-ambientpressure created by a cavity will tend to pick up debris whichaccumulates on the ABS, affecting the configuration of the ABS surfaceand therefore the fly height characteristics of the air bearing. Thepresent invention solves this problem by creating a flow of air throughthe channel 410. The air flowing through the channel will travel acrossthe swept back edge of the cavity as it flows toward the trailing edge.This flow of air flushes debris from the ABS and prevents accumulation.

[0040] With further reference to FIG. 4, each of the side rails 406 isprovided with a front pad 414, located toward the front end of the siderail. The front pads 414 create a high pressure area thereunder whichtends to lift the read/write head 400. In addition, the location of thefront pads controls the pitch of the head 400. Locating the front padscloser to the front end of the rail will decrease pitch, whereas movingthem further back will increase pitch.

[0041] Disposed midway along the length of each side rail is a centralpad 416. The central pads extend along a portion of the inner edge ofeach side rail 416 at the boundary of the cavity 412. The central padscreate further positive pressure for lifting the read/write head 400 andhave a curved, swept back shape which increases performance when theread/write head is at a skewed angle.

[0042] With further reference to FIG. 4, beyond the central pads 416,the side rails extend further toward the back end of the ABS 402 to formtrailing portions 418. The trailing portions end along the lateral edgesof the ABS 402 and terminate near the back or trailing edge 405 of theABS 402.

[0043] The trailing portions 418 of the side rails 406 terminate in rearpads 420, one on each side rail. The trailing portions 418 and rear pads420 act to stabilize roll and help optimize the fight profile of the ABSduring use. It is believed that separating the central pads from therear pads along the trailing edge portion allows air to bleed throughthe separation, which provides a uniform pitch at varying speeds andskew angles experienced between the outer and inner diameter of thedisk. An ABS not having rear pads will exhibit an excessive pitch, of200 to 300 radians. The rear pads have a generally oval shape and aresmaller than the front pads 414 or central pads 416.

[0044] While it will be appreciated by those skilled in the art that thepresent invention can be practiced on ABSs of various dimensions, in thepreferred embodiment of the invention the front and central pads 414 and416 respectively (FIG. 4) extend 30 to 120 micro inches from the baseelevation 404 and 3 to 12 micro inches from the tops of the rails 406.Similarly, the rear pads 420 extend 30 to 120 micro inches from the baseelevation 404 and 3 to 12 micro inches from the elevation of the gap418.

[0045] Centrally located between the lateral sides of the ABS adjacentto the trailing edge 405 is the trailing edge pad 408. The trailing edgepad of the preferred embodiment includes a raised step 422, definingthereabout on three sides a shallow area 424. A profile of the step isshown with reference to FIG. 5. The step 422 extends 30 to 120 microinches from the base elevation 404 and 3 to 12 micro inches from the topof the trailing edge pad 408. In the preferred embodiment the step 422is formed with a ramped trailing edge 426 which slopes gradually to thetrailing edge pad 408. The trailing edge pad 408 and step 422 create ahigh pressure area thereunder, acting to lift the read/write head 400during operation of the disk drive. The pressure under and directly infront of the step is higher than at any other point of the ABS, andaccounts for the majority of the lift. The tailing edge pad 408, andstep 422, improve the fly height profile and are critical to properoperation of the air bearing over a high range of skew angles. Analternate embodiment of the step which does not have a tapered trailingedge portion is referred to as 428 in FIG. 6. In this embodiment thestep is provided with a notched trailing edge 430 which acts to increasethe pitch of the read/write head 400 slightly by creating a slightsub-ambient pressure at the trailing edge.

[0046] With reference to FIG. 7, which shows a profile of the ABS 402,the transitions 702 between the base elevation 404 and the rails 406 andbetween the base elevation 404 and the step 408 are in the form ofsmooth ramps having a nominal slope of 10 degrees from vertical. Thesame is true of the transitions 702 from the rails 406 and the pads 414and 416 as well as the pad 408 and step 422. These smooth transitions702 promote the controlled high pressures necessary for flying the ABS402 and facilitate manufacture.

[0047] With reference to FIG. 10, the performance improvement providedby the present invention can be appreciated. FIG. 10A illustrates theunload characteristics of an air bearing of the prior art. FIG. 10B, onthe other hand, illustrates the improved unload performance of the airbearing of the present invention. FIGS. 10A and 10B show that themeasured load normal to the surface of the recording medium increases asthe air bearing is unloaded. This load reaches a steady state atapproximately 2.5 grams which corresponds to the static load applied bythe suspension.

[0048] However, FIG. 10A illustrates a spike in the unloadcharacteristics of the prior art air bearing followed by an abrupt drop.This spike corresponds to the start of dimple separation. The subambient force holds the slider down while the suspension keeps going upthe ramp. Finally, the sub ambient force is reduced to zero, whichresults in a large drop in measured load. This change in load is calledthe unload or lift-off force. When minimized, it can drastically reducedamage to the suspension arm, as well as reduce the possibility ofhead-disk contact. With reference to FIG. 10B it can be appreciated thatthe unload history of the present invention is advantageously verysmooth, with no apparent sign of dimple separation.

[0049] With reference to FIG. 8, a process 800 for manufacturing the ABS402 of the present invention begins with providing a ceramic substratein a step 802. By way of example, the ceramic substrate can beconstructed of Al₂TiC₃, and is polished in a step 804 to provide asmooth flat surface. The polished substrate can then masked in a step806 as part of a reverse lithography process. The masked substrate canthen be exposed, in a step 808, which causes the exposed portions toharden, prior to etching in a step 810. During the etching process, theportions of the ABS 402 which have not been exposed to the radiationwill be removed at a faster rate than the exposed portions, therebycreating the desired shape. It will be appreciated by those skilled inthe art that the first etching process will produce the pads 414, 416and 420 as well as the step 422. A second photolithography step 812 willbe necessary to create the rails 406 and trailing edge pad 408.

[0050] With reference to FIG. 9, in an alternate embodiment 900 of theinvention, the central pads 416 and rear pads 420 are connected by abridge 902. This embodiment affects the flight profile by increasing thepitch.

[0051] In summary, the present invention provides an ABS which promotesload and unload by reducing the sub ambient pressure during unloading ofthe read/write head. The ABS also exhibits a stable flight profile overa wide range of disk speeds and skews. While the invention has beendescribed in terms of several preferred embodiments, other embodimentsof the invention, including alternatives, modifications, permutationsand equivalents of the embodiments described herein, will be apparent tothose skilled in the art from consideration of the specification, studyof the drawings, and practice of the invention. The embodiments andpreferred features described above should be considered exemplary, withthe invention being defined by the appended claims, which thereforeinclude all such alternatives, modification, permutations andequivalents as fall with the true spirit and scope of the presentinvention.

What is claimed is:
 1. An air bearing surface having a proximal and adistal end defining there between a length and having a pair of lateralsides, the air bearing surface comprising: a first and a second lateralrail extending from a point near said proximal end and terminating at apoint short of said distal end, and defining there between a channelhaving a distal end; a cavity formed between the first and second railsand having a proximal edge connected with the distal end of the channelat a predetermined distance from the proximal end of the air bearingsurface, the predetermined distance being at least 10 percent of thelength of the air bearing surface; a first and second leading edge padformed on said first and second lateral rail near said proximal end; afirst and a second center pad formed on said first and second lateralrail respectively; and a central trailing edge pad generally centrallydisposed between said lateral sides toward said distal end of said airbearing surface.
 2. An air bearing surface as recited in claim 1 furthercomprising a first and second rear pad disposed at a distal end of saidlateral first and second rails respectively.
 3. An air bearing surfaceas recited in claim 2 wherein said first and second lateral railsfurther comprise a first and a second relatively narrow bridge portionextending from said first and second central pad to said first andsecond rear pad respectively.
 4. An air bearing surface as recited inclaim 3 wherein said first and second bridge portions are generallyparallel with said lateral sides.
 5. An air bearing surface as recitedin claim 1, wherein said first and second central pads are elongatedhaving proximal and distal ends, and wherein said distal ends of saidcentral pads are closer to said lateral sides than said proximal ends.6. An air bearing surface as recited in claim 1 further comprising araised portion on said trailing edge pad.
 7. An air bearing surface asrecited in claim 1 wherein the predetermined distance is at least onefourth the length of the air bearing surface.
 1. An air bearing surfacehaving proximal and distal ends defining a length there between, andhaving a pair of lateral sides, the air bearing surface comprising: alongitudinal channel having a predetermined lateral width, centrallydisposed between said lateral sides and extending from said proximalend; said longitudinal channel opening into a cavity at a distance fromthe leading edge of at least 15 percent of the length of the air bearingsurface, said cavity having a greater lateral width than said channel;and a pad, centrally disposed between said lateral sides at said distalend of said air bearing surface.
 2. An air bearing surface as recited inclaim 1 wherein said channel has a maximum width more twice said widthof said channel.
 3. An air bearing surface as recited in claim 1 whereinsaid channel becomes increasingly wider toward its distal end.
 4. An airbearing surface as recited in claim 1 further comprising first andsecond leading edge pads toward said proximal end near said lateralsides.
 5. An air bearing surface as recited in claim 4 wherein saidcavity has first and second edges, said air bearing surface furthercomprising a first and second central pad located along said first andsecond edges respectively.
 1. A method for controlling suction andflight profile characteristics of an air bearing, the air bearingincluding an air bearing surface having proximal and distal ends and apair of lateral sides, said air bearing further having a longitudinalaxis extending from said proximal end and said distal end, the methodcomprising the steps of: providing said air bearing surface with a pairof laterally opposed longitudinal rails extending from said proximal endand defining a channel there between, said channel of a predeterminedwidth; adjusting said predetermined width until a desired suction isachieved; forming in said first and second rails a cavity connected withthe channel at a location a predetermined distance from the proximal endof the air bearing surface; adjusting said predetermined distance untila desired center of suction is achieved.
 2. A method for controllingsuction and flight height as recited in claim 1 further comprising thestep of adjusting the depth of said channel.
 3. A method for controllingsuction and flight height as recited in claim 1 further comprising thestep of providing a front and a back pad on each of said first andsecond rails at the proximal and distal ends thereof respectively.